The present invention relates to a tuning control system of a radio receiver. More particularly, the invention relates to a tuning control system of a radio receiver, which tuning control system permits electronic preset selection.
Tuning of a currently used radio receiver to a desired broadcast frequency is accomplished by changing the inductance or capacitance of a tuning circuit through operation of the tuning knob. Tuning is also provided by previously storing several desired broadcast frequencies via a plurality of push-button mechanisms corresponding to the mechanical position of the inductance or capacitance elements of the tuning circuit, whereby only one of the stored frequencies is mechanically selected.
The latter configuration is well known as the push-button type tuning receiver and is often installed in an automotive vehicle because it permits preset selection. However, the radio receiver of a vehicle must be of small size, and the number of stations for preset selection is limited in a radio receiver in which present operation is performed mechanically, as in a receiver of the latter type, as hereinbefore described. Furthermore, it is usually possible to set only five stations, at the most. For this reason, the push-button mechanism for presetting cannot cover the receiving area when such receiving area changes or spreads out with the movement of the vehicle. In such a case, therefore, the preset condition is once cancelled and setting is then required again. This is very inconvenient. In addition, an automatic tuning receiver is also utilized in the radio receiver of the vehicle, in which tuning receiver a semiconductor variable capacitance element is used for the tuning circuit. A variable control voltage for the variable capacitance element is changed continuously by a potentiometer, and the received frequency is thereby automatically swept and is sequentially tuned to the broadcast frequency.
This type of receiver is very convenient, since all stations within the receiving area may be selected automatically. However, the receiver also has the disadvantage that a considerable time is required for receiving a desired station, when there are many adjacent stations, because tuning is accomplished sequentially, station by station, and includes all stations. Furthermore, it is necessary to operate the selection switch each time the receiver is tuned to a certain station.
As hereinbefore described, the push-button type tuning receiver may immediately select the desired station, but cannot cover the entire receiving area, while the automatic receiver may receive the signal for the entire receiving area, but cannot immediately receive the desired station. Therefore, neither of the receivers hereinbefore mentioned can satisfy the requirements of a vehicular radio receiver, due to their respective advantages and disadvantages.
A tuning control system which eliminates the aforedescribed disadvantages is disclosed in U.S. Pat. No. 4,004,232, issued to Yuji Amaya on Jan. 18, 1977 for Radio Receiver Tuning Control System. In the disclosed tuning control system, a local oscillator signal is extracted from the local oscillator of the receiver and is then converted into a receiving frequency. The converted signal is counted and the counted value is compared with a value corresponding to the desired preset station frequency, digit by digit. The local oscillator is automatically controlled in accordance with the result of the comparison, so that the counted value coincides with the preset value. This is called a digital tuning receiver. The disclosed system may immediately select the desired station over the entire receiving area.
However, the tuning control system disclosed in the United States patent has the disadvantage that presetting is impossible if the desired broadcast frequency is unknown, since the desired broadcast frequency is preset after conversion into binary code via a digital switch, or a value corresponding to the broadcast frequency is stored after conversion into a digital signal via a diode matrix circuit. Furthermore, in the latter case, there is the disadvantage that the preset value cannot be easily corrected.
The principal object of the invention is to provide a tuning control system of a radio receiver, which system may freely preset a desired broadcast frequency.
An object of the invention is to provide a tuning control system of a radio receiver, which system permits easy correction of the preset value.
Another object of the invention is to provide a tuning control system of a radio receiver, which system utilizes a random access memory for presetting a value corresponding to the desired broadcast frequency, thereby reducing the size of the radio receiver by incorporation of electronic preset equipment.
Still another object of the invention is to provide a tuning control system of a radio receiver, which system utilizes electronic preset selection of broadcast frequencies.